2018-05-30_PERMIT FILE - C1981022A

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Serim - 2.05.6 to decreaze az available soluble chemical constiruenu are depleted and chemical concentrations in the • mine water and the exposed rock reach equilibrium Gradual filling of the mine workings will also Gave a beneficial water quality effett, displacing oxygen and reducing the oxidation potential az flooding of the abandoned workings occurs. As described in Section 2.4.7, Hydrologic Description, ground water in both the permit and adjacent areaz is a weak calcium-sulfate or sodiurrrsulfate chemical type. Increazes in both sodium and sulfate constiruenu will not change ground water chemistry although they could result in a shift toward a more dominant ground water type. While various chemical constituenu of the ground water may increase az a result of mine drainage, these increases will not effect ground water use. Due to the limited volume of ground water drainage relative to total flows within the ground water bazin, minor changes in ground water chemistry and levels of certain cotutiruenu are not expected to significantly effect overall ground water quality. Use of ground water from the permit and adjacent areaz is very limited due to the availability of more accessible and higher quality surface water sources. OMI's planned nesting and related attivities are not expected to have any significant long-term effect on recharge, storage, or discharge relationships. As described in Section 2.04.7, Hydrologic Description, recharge within the ground water basin occurs primarily along the outcrop of the vazious stratigraphic uniu az a result of direct precipitation and infiltration in outcrop areas. OMI's operations are both limited in areal extent and are not located within any major recharge area. Drainage of the stored mine water system during mining operations will effect ground water storage relationships. This effett, however, will be localized and temporary. Upon completion of operations and mine reclamation and closure, ground water will once again accumulate in the mine workings and ground water storage relationships will be reestablished. Discharge relationships will ako be minimally effected with some temporary reduction in downgradient ground water flows az a result of • filling of the underground mine workings az well az localized alterations in ground water flow patterns. The quantity of ground water discharge which will be effetted u a relatively small percentage of the total volume within the ground water basin. The existing Somerset and Sanborn Creek mine workings and proposed Elk Creek workings progress down-dip from the mine portals and mine drainage u controlled during active operations, so there is little or no potential for direct gravity discharge of water from the mine. On completion of mirtirtg and related activities, however, mine drainage control operations will cease and portions of the mine workings (especially the mine workings furthest down-dip) are expected to gradually fill az continuous ground water inflows discharge to the mined-out areas. Bazed on the Jack of any significant base-flow in Elk Creek and absence of shallow ground water in test borings in the portal area, the natural water table is below the portal elevation and mine water discharge from the E& Creek Mate portals is not anticipated. To assure that there will not be any significant discharge from the mine openings following cessation of active mining operations and mine closure, OMI will sea] and bacldill the mine portals. Sealing prattices are discussed in Sections 2.05.4, Reclamation Plan, and later in this section under the heading, Reclamation of 1vLne Disturbance Areas. Water will not be diverted or discharged into any other underground mine in conjunttion with OMI's ongoing mining and reclamation operations. The only anticipated potential ntirtirtg-related impact on water righu and use would be minor reductions in flows to the North Fork due to mine water supply whdrawa]s az previously addressed under the sub-heading, MInor Reductions in Surface Flows and Alteration of Surface Flow Patterns Due to Operation of Sedimentation Structures and Flow Reductions Due to 1vLne Water Supply Withdrawals. As noted in the referenced discussion, both the average annual and ma~**~ttm anticipated water supply withdrawal rates represent a very small percentage of total flow volume for . the North Fork Mme drainage, which does not result in any reduction in surface flows due to the lack of a direct hydraulic connection, will probably result in some variable discharge of excess mine water to the surface system, effectively augmenting surface flows on a year-rotmd bazis. While mining and related subsidence may impact overlying perched aquifers and any associated seeps or springs, as previously discussed under the sub-heading of, Drainage of Seeps and Springs, water righu PR04 2.05-96 Revised May 2001